The present invention generally relates to a method and apparatus capable of measuring the mass of a specimen by subjecting the mass to a vibrational load and comparing the measured frequency of vibration to frequencies of known masses. In particular, the present invention is directed to an apparatus for determining the mass of a specimen located in a microgravity environment. Such a microgravity environment will exist on the International Space Station (ISS) or any craft in near Earth orbit.
A problem confronts scientists when attempting to monitor the mass of a quantity of fluid present in a container located in a microgravity environment. For example, on the ISS it would be difficult to economically monitor the changing mass of a life-sustaining fluid because the mass of the fluid could not be accurately determined due to the microgravity. There is no known approach which utilizes information obtained in a gravity environment to determine the mass of a specimen located in a microgravity environment. Whether the test specimen is in fluid or solid form, the problem of determining the mass microgravity has proven difficult if not impossible.
There clearly is a need for a measuring apparatus and method capable of determining the mass of a test specimen maintained in a microgravity environment. There is also a need for a measuring apparatus capable of repeatedly providing accurate readings regardless of changes in the mass or its environment. There is, moreover, a need of a measuring apparatus, i.e., scale, that is compact in size, of minimum weight and as economical as possible to construct.
In one aspect of the present invention recognizes a mass of a test specimen is measured by subjecting the mass to either a constant vibrational load i.e., forced vibration, or by subjecting the mass to a mechanical impulse i.e., free vibration. In either instance, the specimen vibrates at a specific frequency indicative of the mass of the specimen. By performing a number of similar tests in a gravity environment, it is possible to determine the calibration frequencies achieved by a number of specimens of differing mass. By comparing the frequency of the specimen tested in the microgravity environment with the set of pre-determined frequency calibration curves established for known masses, the mass of the test specimen is determined.
In another aspect of the present invention, a test specimen located in a microgravity environment and having a mass to be determined is attached to a freely vibrating spring. As the spring is repeatedly vibrated, a sensor measures the frequency of vibration. By calculating the spring constant and referring to a previously determined spring constants for given masses, it becomes possible to determine the mass of the test specimen
In another aspect of the invention, a test specimen located in microgravity is contained within a tank attached to a vibrating mount. The tank also includes a pressurized gas separated from the fluid test specimen by a flexible member which may take the form of a bellows or a bladder. The vibrating mount repeatedly oscillates in order to determine the natural frequency of vibration of the mount, from which the spring constant of the mount can be calibrated. This, in turn, may be used to determine the mass of the test specimen.
In a yet further aspect of the present invention, a fluid specimen located in a microgravity environment is located within a tank including a bellows and pressurized Nitrogen on the other side of the bellows. The vibrating mount takes the form of a cantilevered beam bolted at one end to a rigid structure. During operation, a sensing element achieves maximum sensitivity in monitoring the frequency of vibration of the vibrating mount, the tank and the fluid test specimen. A device referred to as a xe2x80x9cpingerxe2x80x9d supplies a mechanical impulse to induce a natural frequency of any object to which the pinger is attached. The pinger serves to oscillate the vibrating mount, thus providing xe2x80x9cin situxe2x80x9d readings of the undamped natural vibration frequency of the tank and fluid test specimen.
In order to determine the mass of the fluid, the spring constant of the vibrating mount is first calculated with a known mass and measured frequency of natural vibration of the mass. The unknown mass of fluid can then be determined by comparing the frequency of vibration of the test fluid with the frequencies of vibration of known masses. Preferably, known frequencies may be used to create a set of frequency calibration data. Though the spring constant of the of the vibrating mount and tank may vary slightly through differing amplitudes under differing gravity conditions, these minor variations may be easily compensated for in the set of pre-determined calibration curves.
In another aspect of the present invention, a method is disclosed for measuring the mass of a test specimen located in a microgravity environment. The specimen may be mounted on the free end of a spring member having an opposite end attached to a rigid member. As the spring and mass are forced to vibrate, a sensor measures the natural frequency of vibration. The spring constant may then be calculated and knowing the frequency of vibration for known masses utilizing a spring with the same constant, it is possible to determine the mass of the test specimen.
In another aspect of the present invention, a method is disclosed for measuring the mass of a fluid in a microgravity environment. The fluid may be deposited in a tank on one side of a flexible member which take the form of a bellows or a bladder with a pressurized gas located on the opposite side of the bellows to maintain pressure on the fluid. The tank may be attached to the free end of a cantilevered spring which is forced to vibrate. A sensor is positioned to monitor the frequency of vibration, allowing the spring constant to be determined. This can be compared to the vibration of known masses in a full gravity environment under a spring with the same constant to determine the mass of the fluid.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.